Formalise "rhizome add file" exit status

Formalise add-bundle result in "enum rhizome_bundle_status"

Rewrite rhizome_manifest_finalise(), rhizome_find_duplicate() and
rhizome_add_manifest() to return enum rhizome_bundle_status

New function rhizome_manifest_check_stored() that compares a manifest
with its stored counterpart and returns enum rhizome_bundle_status

Remove redundant rhizome_manifest_check_sanity(), consolidating all
manifest validation rules in rhizome_manifest_validate(), which now
checks the 'id' field is present, and that 'sender' and 'recipient' are
both present for MeshMS

Correct manifest finalisation logic: set the 'finalised' flag in
rhizome_manifest_validate(), not in rhizome_manifest_verify() (which
sets 'selfSigned'), and consistently clear 'finalised' flag in all
attribute setter functions

Remove manifest 'ttl' field and all references thereof (leaving unused
space in Rhizome BAR)

Rename some payload functions for clarity
UNFINISHED Implement HTTP POST /restful/rhizome/insert